A conventional pneumatic power tool comprises a spindle with a socket into which a drill bit may be inserted. The spindle is conventionally driven by two separate gears, which are normally arranged as sleeves coaxially around the spindle. A first gear, the drive gear, is arranged in axial splines in order to drive the rotation of the spindle. The second gear, the feed gear, is threaded onto the spindle such that the mutual rotation between the feed gear and the spindle creates an axial movement there between that feeds the spindle in an axial direction. The feed gear may be geared so as to either advance or retract spindle.
Conventionally, the spindle is advanced in that the threaded feed gear rotates at a slightly higher rotational speed than the spindle. When the drilling operation is concluded the feed gear is positioned into an angularly blocked position. Thereby, as the feed gear is blocked from rotation, the continued rotation of the spindle with respect to the feed gear will rapidly retract the spindle back to its initial position.
A problem inherent in such conventional pneumatic power tools is that the spindle and/or the gear that feeds the spindle might get jammed due to the relatively high rotational speed of the spindle and the gears. This is troublesome not only because it implies that the jammed part needs to be loosened, but also because the parts of the tool will be exposed to heavy stress and wear.